1. Field of the Invention
This invention relates to a linear guide apparatus for guiding a movable body, such as a table, in a machine tool.
2. Description of the Related Art
In machine tools, sliding guides and rolling guides are primarily employed in guide mechanisms for movable bodies, such as columns, spindle heads, tables, etc.
Sliding guides, in which a sliding member makes a sliding contact with a guide surface, have a high static rigidity and, as compared to rolling guides, are excellent in damping of vibrations that could cause fluttering.
On the other hand, rolling guides, which utilize a rolling contact between a rolling member and a guide surface, have a low vibration damping capacity. Because of low frictional force, however, rolling guides are superior in high speed and motion accuracy to sliding guides. Thus, sliding guides and rolling guides have advantages in terms of each other's disadvantages, and have disadvantages in terms of each other's advantages.
Linear guide apparatuses have recently been developed which, with a view to compensating for the drawback of rolling guide, employ a braking mechanism, etc. in a rolling guide to generate a frictional force, thereby enhancing the damping capacity of the rolling guide. Such conventional linear guide apparatuses include an apparatus in which an elastic bag is expanded by air pressure so as to press a damping plate against a brake rail (see Japanese Patent Laid-Open Publication No. 1997-217743), an apparatus in which a brake plate is deformed by the action of a pressurized fluid so as to press the plate against a track rail (see Japanese Patent Laid-Open Publication No. 1997-329141), and an apparatus in which brake shoe is pressed against a guide rail by means of a hydraulic biasing device (see Japanese Patent Laid-Open Publication No. 2000-9655).
The conventional linear guide apparatuses thus utilize either a hydraulic pressure or air pressure to apply a load to a rail so as to generate a frictional force, which necessarily makes the braking mechanism for enhancing vibration damping complicated. Further, with such a breaking mechanism, a gap may be formed between a braking or damping member and a guide rail. The presence of even a very small gap causes an uncontrollable minute displacement of the braking or damping member in the gap direction, whereby the desired damping capacity cannot be obtained.